1. Field of the Invention
The present invention relates to dissolution testers. More particularly, the present invention relates to apparatus measuring the rate of dissolution of materials such as pharmaceuticals, particularly those in pill or capsule form.
2. Description of the Related Art
Dissolution testing is used to determine the rate of dissolution of pharmaceuticals in dosage forms in specific test solutions to simulate digestion in a human or animal. The requirement for such dissolution testing apparatus is provided in United Sates Pharmacopoeia(USP), Edition XXII, Section 711, Dissolution(1990).
Conventional dissolution testers have one or more test vessels in the same apparatus where the test solution may be placed. For each test vessel, there is a stirring device. As described in USP method I, a basket-type stirring element consisting of stainless steel(SS) shaft with a cylindrical basket at its lower end is specified. As described as USP method II, a paddle-type stirring element consisting of SS shaft with an SS blade at its lower end is specified.
As per USP requirement, the test solution placed in the dissolution vessel must be maintained at a constant 37xc2x0 C. For the conventional dissolution tester, the dissolution vessel is placed in a temperature controlled water bath. Heat is transferred to the vessel solution by means of the water bath. This conventional process is time-consuming; it takes more than an hour to heat the solution to the desired temperature. Water baths also have inherent problems such as leakage, evaporation, and algae growth. A water bath requires a considerable amount of water which requires heating. This process leads to excessive electric power consumption. In addition, water bath apparatus requires draining and cleaning. After cleaning, the bath must be refilled and heated to the desired temperature, a time-consuming task.
As per USP dissolution testing procedure, the test vessel solution temperature must be measured before the test is initiated. It is not permitted to put a temperature thermometer into the test vessels during the dissolution test. For conventional dissolution testers, the dissolution-testing operator measures only the water bath temperature during the test, itself. As a result, there are no direct temperature measurements of test vessels during the testing process, thus there is no true temperature data.
As per USP specification, all thee solution in the test vessel must be degassed. In conventional dissolution testing apparatus the operator must degas the test solution before it is poured into the dissolution vessel. The degassing is performed by heating, stirring or by vacuum techniques. This is an additional task which must be carried out by the operator.
The problems, then, associated with a conventional dissolution may be summarized as follows: (1) non direct heatxe2x80x94it takes too long to heat the test vessel solution to desired temperature; (2) energy wastexe2x80x94substantial energy is required in heating extensive amounts of water solely for heat transfer; (3) time consumingxe2x80x94it takes substantial time to clean the bath, maintain clean water at the desired temperature, avoid leakage, compensate for evaporation, and perform required maintenance; (4) lack of direct temperature dataxe2x80x94there is no means to measure the actual test vessel temperature during the dissolution testing procedure (temperature is critical in dosage dissolution rates); (5) degassing requiredxe2x80x94the operator must degas the test solution.
It is desirable, then, to have an improved dissolution tester, exhibiting: (1) a faster heat up time, thus increasing productivity; (2) elimination of a water bath for solution heating; (3) providing direct test vessel temperature data throughout the test; and (4) elimination of the solution degassing step.
U.S. Pat. No. 5,589,649, issued Dec. 31, 1996, to Brinker et al., describes a rotating paddle type dissolution testing apparatus featuring a heater and temperature sensor for each test vessel. The heating elements are wrapped around the outside of the test vessels. Each stirring element has a hollow shaft in which the temperature sensors are placed. The ""649 patent would necessarily experience difficulty in maintaining a uniform temperature using direct heating elements due to inherent difficulties in mechanical heat transfer and the maintenance of the heating elements.
U.S. Pat. No. 5,540,496, issued Jul. 30, 1996, to Beckett et al. describes a dissolution test flow cell featuring a heater-circulator 55 in FIG. 1, thereof.
U.S. Pat. No. 5,055,273, issued Oct. 8, 1991, to Wilhelm et al. describes a hollow, heatable stirrer for use with viscous liquids in a reactor or mixer.
U.S. Pat. No. 3,802,272, issued Apr. 9, 1974, to Bischoff et al., describes a dissolution test apparatus employing a rotating basket type tablet holder.
U.S. Pat. No. 4,856,909, issued Aug. 15, 1989, to Mehta et al. describes a basket type dissolution tester featuring a solvent-containing glass beaker heated by a thermostatically-controlled bath for holding the temperature of the solvent at about 37xc2x0 C.
U.S. Pat. No. 5,816,701, issued Oct. 6, 1998, to Martin et al. describes a dissolution tester featuring standard beakers, each surrounded by an aluminum platen containing heating elements, and featuring a thermistor for measuring the platen temperature, the heating elements being controlled by means of a computer responsive to the thermistor. The solution in the beaker may then be controlled at the desired temperature for the dissolution test. The ""701 patent platen would appear to take a substantial length of time to reach a uniform desired temperature.
U.S. Pat. No. 5,412,979, issued May 9, 1995, describes a typical paddle type dissolution vessel having an internal solution and a liquid heating bath.
None of the above inventions and patents, taken either singularly or in combination, is seen to describe the instant invention as claimed. Thus, an air bath dissolution tester solving the aforementioned problems is desired.
The present air bath dissolution tester solves the above-mentioned problems. It provides a heating element within the USP specification dissolution test stirring shaft, the shaft being configured to be easily attachable to a basket-type (USP) method I or paddle (USP method II). This allows direct heat transfer to the test solution in the vessel directly, reducing the time required to heat the test vessel solution to the desired level. Temperature in the vessel is controlled by placing a surface sensor on the outside wall of the test vessel, preferably near its base, allowing temperature data to be displayed and recorded during the test and serving as a sensor for an automatic control system which maintains the test vessel temperature during dissolution testing. The test vessel is located in an air chamber to prevent heat loss. The air chamber functions a heat jacket, keeping heat in the test vessel and separate from cool environmental air. The air chamber is transparent, so the operator can see through the air chamber wall to check the motion of the stirring device and the dissolving dosage during the dissolution test. This allows for the total elimination of the requirement of a water bath. The heating element in the SS shaft promotes test solution degassing by direct heating and high-speed stirring while the test solution is being heated to operating temperature, thus eliminating a separate step.
Accordingly, it is a principal object of the invention to provide a dissolution tester apparatus having rapid heating to operating temperature, resulting in increased productivity.
It is another object of the invention to provide a dissolution tester apparatus which requires no water bath.
It is a further object of the invention to provide a dissolution tester apparatus which allows the direct measure and recording of the test vessel solution temperature.
Still another object of the invention is to provide for direct heating of the test vessel solution and the automatic control of the solution during a dissolution test.
Yet another object of the invention is to provide for degassing of the test vessel solution during the heating period, thus eliminating a separate step.
Still another object of the invention is to provide an apparatus as above which meets the requirements for dissolution testing apparatus as provided for in the USP.
It is an object of the invention to provide improved elements and arrangements thereof for the purposes described which is inexpensive, dependable and fully effective in accomplishing its intended purposes.
These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings.